Sag-resistant fiberboard panel and method of making the same



May 12; 1970 F. GARRETT, JR V3,511,744.

' SAGRESISTANT FIBERBOARD PANEL AND METHODV OFMAKING THE SAME Filed July 27, 1965 INVENTOR FRED GARRETT, JR-

ATTORNEY ET mw 5P. A1C?- L United States Patent O ABSTRACT F THE DISCLOSURE A method of producing a sag-resistant fiberboard by the steps of forming a brous slurry and then forming from the slurry a wet board having at least two primary surfaces. The board is partially dried, then abrasively treated atleast on a portion of one of the primary surfaces. The other primary surface is coated with a sagresistant material on at least a portion of its surface.

Finally, a decorative coat of material is placed over the abrasively treated surface. The coaction of the abrasively treated surface on one side of the board and the sagresistant material on the other side of the board cause the board to assume a cupped appearance in -the direction of the abrasively treated surface. The board, when used as .a ceiling panel suspended by its edges, would then sag causing the cupped appearance to disappear and the board to assume a atoappearance.

Many problems have been encountered in the fiberboard ceiling tile and panel field with regard to the sag resistant properties of such items. The most serious problems occur in edge supported 2' X 2', 2 x 4 or larger panels which are located in hot, humid areas. Further, panels of wood fibers generally are more susceptible to sag than panels of mineral fibers due to the water absorbing capability of wood fiber. However, in both cases of wood and mineral liber, the binder utilized in such panels may be water absorbent and therefore, subject to sag.

Several solutions to the problem of sag in such fiberboards have been set forth. U.S. Pat No. 3,147,156 discloses two types of treatment which may be utilized to minimize sag in mineral fiberboard. One approach is an nternaljreatment of the binder with a magnesium compound such as MgO. The other approach mentioned in this patent is an external treatment involving a face coating of a moisture-resistant, thermosetting resin such aslnelamine formaldehyde, for example.

U.S. Pat. No. 3,092,508 discloses a method of treating I fberboard wherein said fiberboard is coated with a thermosetting material and then molded into cup-shaped yform prior to complete setting of the coating material. Thensuch a board is removed from the mold and permitted to atten. Thereafter, the-treated board is said to -have little tendency to sag.

The method and article of the present invention providemimproved sag resistant characteristics for fiberboard v pauelsby combining an abrasive treating operation such as sanding on one surface of a panel with a sag resistant coating treatment of thesurface of the panel opposite to that which had been sanded.

Accordingly, an object ofthe present invention is to provide a method of treating fiberboard to produce a fberboard panel having improved sag resistant characteristicS.

Other objects of the present invention will be readily apparent from the detailed description hereafter with reference to the drawings wherein FIG. 1 is a diagrammatic view in three sections of one 3,511,744 Patented May 12, 1970 ice embodiment of apparatus which may be used to carry out a method according to the present invention; and

FIG. 2 is a view in perspective of a berboard which has been subjected to the operation included in the method of the present invention.

Referring now to FIG. 1, there is shown a conventional board forming machine 20 having a screen-covered, vacuum cylinder 21 rotatably mounted in a slurry tank 22. Tank 22 contains a fibrous slurry 23 which may contain fibers of a cellulosic nature, for example. As cylinder 21 has rotated through slurry 23, the interior of cylinder 21 is connected to a suitable source of vacuum whereupon a fibrous sheet of slurry will be adhered to the outer portion of cylinder 21 as air is pulled therethrough to remove the water from sheet 24 and cause the fibers to be pulled toward the surface of cylinder 21. At point A the vacuum is released, and a doctor blade 25 strips sheet 24 from the surface of cylinder 21.

Sheet 24 is then carried by driven rollers 26 to a conventional screen press 27. Screen press 27 comprises a pair of screen belts 28, one of which is located on each side of sheet 24 and mounted for movement about support rollers 29. A pair of perforate, pressure rollers 30 presses the upper screen belt into contact with the upper surface of sheet 24. The interior of each roller 30 is connected to a suitable source of vacuum. Underlying each roller 30 is an imperforate pressure roller 31 which presses the lower screen belt into contact with the lower surface of sheet 24. Each cooperating pair of imperforate and perforate pressure rollers causes the sheet 24 to be compressed. Moisture is removed from said sheet 24 as said sheet is compressed. This moisture may be carried away with the air passing through the screen belts 28 and through the perforate pressure rollers 30. The direction of movement of the screen belts 28 is indicated by the arrows. As the sheet 24 leaves the screen press 27, the upper and lower surfaces of said sheet 24 retain impressions imposed by the screen belts 28. However, the impressions on the lower surface of sheet 24 will be substantially erased as sheet 24 passes over and is driven by conveyor rollers 33. Although certain apparatus has been shown and described, other conventional board forming devices may be utilized.

After passing through screen press 27, the sheet 24 next passes under a sag resistant coating supply header 34 which deposits a puddle of sag resistant coating material on the upper surface of sheet 24. A conventional roll coater 36 rotates in the direction of movement of sheet 24 and meters, while pressing, a portion of the coating material onto the sheet 24. It is noted that the roll coater 36 forms a dam for the puddle 35. This coating may be a melamine formaldehyde coating similar to that disclosed in U.S. Pat. No. 3,146,156. However, other resinous, proteinaceous, starch, or other type coatings may be used, depending upon the requirements and amount of sag resistance which is desired, as will be explained in greater detail hereafter. It will be noted that the sag resistant coating 35 may be placed on the sheet 24 when it is essentially still in wet form and contains considerable moisture. Such a coating resists moisture accumulation of the final product.

Subsequent to the coating operation, sheet 24 may be severed into individual boards 37 by saw 38 which may be appropriately mounted to make a transverse cut while sheet 24 is in motion, as is known in the art and shown in U.S. Pat. No. 2,084,980. The board proceeds from the saw 38 into oven 39 on conveyor belt 40. Oven 39 dries the board as well as the coated surface thereof. Upon leaving the oven, each board 37 may be further separated into smaller pieces by means of saw 41, which is positioned to make a longitudinal cut in board 37.

Additional sawing apparatus-may be provided at various .excessive amount of moisture from each board 37, and it has been found that better end results are obtained when the moisture content of each board after drying is restored to an amount between about 2% to 9% in each board. The moisture restoring operation may be accomplished -by water sprayed from headers 42. Since it. has

been found to be desirable to have a relatively uniform moisture content throughout 'each board 37, a storage period may be desirable to allow the water sprayed from headers 42 to permeate the board. In such a case, boards 37 may be stacked upon one another during this storage period.

At the end of the storage period when the moisture ,content of each board has reached a somewhat uniform state, each board is turned over and placed upon conveyor I belt 43 which carries each board under a rough sanding belt 44 and a subsequent, fiinish sanding belt 45. Sanding belts 44 and 45 are set to remove any crust portion on the surface of the board occurring as a result of passing through oven 39. This sanding operation in removing the .as a ceiling panel in a peripheral support system wherein only the edges of the panel are supported, said panel Will tend to flatten to a certain degree depending upon its over-all size but will not assume a convex position or sag under high heat and humidity conditions. Although the sanding operation alone without the coating operation may provide -a certain degree of cupping which is desirable in resisting sag, such cupping in some cases may not be retained or great enough to provide satisfactory results without coating the side of the board opposite to that which has been sanded. In other words, apparently there is some cooperation between the coating on the one side of the panel and the sanding operation on the other such that a desirable degree of cupping is obtained in, and retained by, the panel. In any event, after the boards have been sanded, the surface thereof may be cleaned by a conventional vacuum device 46. A shield 47 may be provided to localize the dust condition. g

Subsequent to the sanding operation, the boards may pass through a conventional coating operation wherein casein oranother conventional type of paint, for example, may be applied to the board by means of top spray nozzle 48 and bottom spray nozzle 49. Thereafter, the boards may be carried by aconveyor 50 through a conventional dryer S1. A function of such a coating is to provide smooth surfaces on the board.

It has been found that each board more satisfactorily retains the desired cupping imparted thereto as a result of the sag resistant coating on one side of the board and the sanding operation on the other side of the board, when a coat is applied to the sanded side of the board. Further, such an operation provides a smoother face on the surface of each board. The final cupped shape of a board is seen more clearly in FIG. 2.

x It has been found that with the method heretofore described,=substantially uniform cupping is provided in each board. Therefore, if the finished board is required to be reduced in size by further cutting operations, each severed segment thereof will still have a cupped con-figuration.

In the fibrous ceiling tile, panel, and board field, it is known to emboss, drill, punch, or combine a number of such operations to produce decorative effects in boards. Each of these operations and especially the embossing operation is believed to weaken the board causing greater sag potential. Thus, the Ifinal cupped conguration of a board so processed may be reduced by any of the punching, drilling, embossing, or other operations. Therefore, the type and amount of sag resistant coating applied and the extent of the sanding operation may be regulated to give the resultant, desired of cupping in the surface,

face, or room side of the tile, board or panel under consideration. Further, the amount of cupping will also depend upon the over-all size and thickness of the board. For example, larger boards could have a greater initial degree of cupping. However, care should be taken to avoid excessive cupping if a substantially at panel installation is desired. It has been found that the resinous type of sag resistant coating and particularly, melamine formaldehyde produces a high degree of cupping when combined with the sanding operation. Thus, when any of the punching, drilling, or embossing operations are used, such a resinous coating may be desirable to give a greater degree of cupping. In this case, the board after passing through any of these operations and having its cupping somewhat reduced thereby will still have an adequate amount of cupping so as not to sag whenA installed in a peripheral support system.

In a case where none of the punching, drilling, or iissuring operations are performed on the board, the melamine formaldehyde or other resinous coating may provide an excessive amount of cupping. In these cases, sag resistant coatings of starches or proteinaceous compositions or other compositions may be used to vary or reduce the extent of cupping of the board.

It is to be understood that the coat applied to the sanded side o fthe hoard as described above may not be the final decorating step. Many other decorative effects have been produced by subsequent operations such as splattering, glittering, stencilling, printing, etc., and may be provided on the boards produced by the subject method.

As noted above, it has been found that the boards produced by the subject method have a degree of cupping such that when each board is installed and peripherally supported, it may settle into a substantially flat position without assuming a convex or sagging configuration even when located in hot, humid areas.

In a specific example, a wood fiber slurry was prepared and sheeted by means of a conventional board forming machine and therafter passed through a conventional screen press. A coating of melamine formaldehyde was then placed on the upper surface of the board with roll coating apparatus in the amount of approximately 36 grams per -square foot. This coating may comprise about five parts of an solution of melamine formaldehyde, 17 parts clay, 58 parts water, and a very small amount of wetting agent on the order of .01 part. This coating was found to penetrate the upper surface of the board. The board then is passed through the first drying operation in a conventional air circulating dryer. The particular point at which the board is severed into transverse and longitudinal sections is not particularly important and may be performed at suitable points during the process. After leaving the oven, the moisture content of the board is raised to about between 2% and 9% by means of a water spray. The boards may then be stacked for a period of time to allow the moisture to permeate throughout the board. The boards are then turned over and passed through the sanding operation wherein approximately 30 to 40 thousands (.0'30-.040") is removed from the upper surface of the board, the final thickness of the board in this case being a nominal 1/2". Thereafter, a conventional casein or other type coating may be applied by the top and bottom spray coaters in the amount of about 11- 21 grams per square foot each. The drying operation may be performed in a conventional oven. lf the board up to this point has not been reduced to the appropriate panel size, it may be so cut at this point. The embossing, punching, or drilling operations, if utilized, usually are performed subsequent to the last mentioned coating operation.

If no mechanical operation such as punching, drilling, or embossing is to be performed on the board, it has been found that it is desirable to substitute a starch coating,

, for example, for the resinous coating noted above to of the method disclosed herein may be used to provide sag resistance in berboard, tile, or panels other than those of'wood or cellulosic fiber. It is believed that the coating and abrasive treating or sanding operations may be applied to any sidev of the board as long as each operation is on the side opposite that on which the other operation has been performed. However, it should be noted that in the case of the wood iiberboard described above, the best results were found to occur when the coating was applied to the side of the board which retained the screen marks or the upper side of the board after it has passed through the screen press. t

It should be noted that the coatings may be applied by conventional apparatus such as brush, spray, roll coat- The method of lthe present invention may be applied to any size of sheet or board, and the term liberboard l as used herein is meant to cover any size of such board including tile or panel size. The sequence of steps of the method according to the present invention may be varied. For example, the sag 6 subsequently coated with sag resistant material and a finish coat or coats.

Various modifications of the present invention may occur to those skilled in the art without departing from the spirit and scope thereof as defined in the claim.

I claim:

1. A method of producing sag-resistant liberboard comprising the steps of forming berboard having at least two primary surfaces, each of which being` located on a side of the board opposite from the other, coating at least a portion of one of said surfaces with a sag-resistant means which helps the berboard resist moisture and prevents expansion of the opposite surface to result in the sagging of the iiberboard, drying said iiberboard in part, then abrasively treating at least a portion of one of said surfaces other than said coated surface to at least partially stress relieve said board by removing the crust portion on the surface of the board formed by the drying of the berboard, whereby the fiberboard, which is abrasively treated on one sideand coated with a sag-resistant means on the opposite side, will be cupped in the direction of the abrasively treated side. l

2. The method of claim 1 further comprising the step of applying a coating of materialto at least a portion of said abrasively treated surface.

3. A sag-resistant berboard product made according to the process of claim 1.

References Cited UNITED STATES PATENTS 2,131,043 9/1938 Harshberger et al. 161-125 2,292,118 8/ 1942 Guhl 117-66 3,092,508 6/1963 Barrett et al 264-137 3,325,302 6/ 1967 Hosfeld 117-8 MORRIS SUSSMAN, Primary Examiner U.S. Cl. X.R. 

